00:01
For this question we are given that we want to set up a bulb system with two filaments such that we will get three different power settings.
00:12
And the only possible way to do this is if the filaments are connected in parallel with each other.
00:18
So assuming a filament is a resistor, we're going to have two switches, one on each of the parallel circuits.
00:37
And with this we will have two elements.
00:40
Three different settings, right? so we can either have the first switch closed, so we'll have current passing through the first resistor r1, or we can have the first switch open, but second switch closed.
00:59
So we'll only have current passing through r2.
01:02
And finally, the third setting is if both of these switches are closed.
01:07
So we have current passing through both r1 and r2.
01:10
2.
01:10
So these three different settings is possible.
01:15
Now we're given that we want these settings to be either 60 watts, 120 watts or 180 watts.
01:24
Now considering this as the entire and entire effective resistance circuit, we know that power is equals to v square over r.
01:36
That is, because the potential drop across the resistor is always the same is always the emf of our source, right, the emf over here...